Flash lamp



y 1961 R. M. ANDERSON 2,982,119

FLASH LAMP Filed April 27, 1959 l4 gpfl /z /2 mai I Invervtor: Rober t M. Ander'son 105 W Hi3 A gtzmwweg.

United FLASH LAIVIP Filed Apr. 27, 1959, Set. No. 808,981

4 Claims. (Cl. 67-31) This invention relates in general to flash lamps of the type comprising a sealed radiation-transmitting bulb containing a loose filling of a readily combustible filamentary material and a combustion-supporting medium, such as an oxygenous gas, Which enters into a reaction with the combustible material with the resulting emission of an instantaneous flash of actinic light of high intensity. More particularly, my invention relates to a midget sized flash lamp of the above general type having an exceptionally high light output per unit volume of the lamp bulb or envelope.

Because of the many attendant advantages of small sized flash lamps, such as increased ease and convenience a in respect to the portability and handling thereof and less cumbersome size of the lamp-holding reflector and associated equipment employed to flash the lamp and redirect the light therefrom onto the object being photographed, it has been the constant aim in the flash lamp art to produce flash lamps which are of smaller size while still affording suflicient light output to be suitable for picture-taking purposes. At the same time, it is desirable that such a smaller size flash lamp be safe in operation, i.e., free from explosion hazard, and that the cost thereof be maintained as low as possible, and preferably lower than that of any previous type miniature size flash lamp available on the market.

As made heretofore, flash lamps have generally employed so-called blown glass bulbs or envelopes, i.e., one made by blowing or expanding a molten charge of glass, or a softened length of glass tubing, into a surrounding mold. However, as an inherent characteristic of such blown glass bulbs 'as made by the conventional manufacturing' procedures employed at present, the bulbs do not possess substantially uniform wall thickness throughout but instead. are characterized by areas of thin wall section as compared to the remainder of the bulb, such thin wall sections generally being located at the sides of the bulb where the outward expansion of the glass into the bulb-forming mold is greatest. Such relatively thin side wall areas adversely affect the safety of a flash lamp for several reasons. For one thing, a high unit tensile stress is developed in the glass of the bulb at such thin wall areas on flashing of the lamp, the tensile stress resulting from the intense heating and attendant great increase -in the pressure of the gas within the lamp by the heat generated in the bulb by the combustion of the combustible material therein. Such higher unit tensile stresses in the glass of the bulb at the thin Wall areas. are therefore more apt to result in the rupture or breakage of the lamp bulb. This is especially so in those cases where there is coupled therewith the added factor of high thermal shock to such thin Wall glass areas resulting from the contact thereof with hot metal particles of the burning combustible material. For another thing, since by far the greatest proportion of miniature type flash lamps are used or flashed while located in a more or less horizontal position, i.e., with the axis of the lamp horizontal,

41f QICEEIII Patented May 2, 1961 the burning metal particles of the combustible material that are ordinarily formed in the bulb on flashing of the lamp will therefore drop down onto the side wall portion of the lamp. Accordingly, where such side wall portion of the lamp bulb is of relatively thin section, as in the case of the conventional type blown glass bulbs, the contact of the burning metal particles with such thin side wall sections of the bulb is therefore more likely to cause the cracking thereof, with resultant shattering or explosion of the bulb itself.

The combustible material heretofore generally employed in miniature type flash lamps as the light-producing source therein generally consisted of a loose filling of filamentary wire or so-called shredded foil consisting essentially of aluminum or zirconium. The burning characteristics of these aluminum and zirconium type filamentary combustible materials are quite different, however. Thus, when aluminum combustible material is ignited within a flash lamp, many hot burning particles or globules of aluminum are formed therein and are forcefully propelled in all directions within the bulb at high velocities. Consequently, where the bulb is of too small a size to allow these hot burning aluminum particles to either travel a sufficient distance in the bulb to be completely consumed before they strike the bulb wall or else to lose a sizeable amount of their velocity, the burning aluminum particles will then strike the glass bulb wall with a considerable force of such magnitude that, coupled with the softening effect which the hot metal particles exert on the glass, actually results in their penetrating through the glass bulb wall with the resulting likelihood of causing either the glass bulb to explode or shatter, or the outside protective lacquer on the bulb to catch on fire. In contrast thereto, the zirconium type filamentary combustible material has the property of burning more or less in place Within the lamp bulb, without the formation of hot burning metal particles and the forceful propelling thereof at high velocity throughout the interior space of the bulb and into forceful contact with the glass wall thereof. In consequence thereof, a zirconium type filamentary combustible material is not nearly as likely to cause the cracking or shattering of the glass lamp bulb, or the ignition of the outside lacquer thereon, as an aluminum type filamentary combustible material.

For the above reasons, therefore, the use of so-oalled blown glass bulbs for flash lamps as has been the common practice heretofore, and particularly when coupled with the use of filamentary combustible material composed essentially of aluminum, has placed an arbitrary limitation on the amount of combustible material and combustion-supporting gas filling which could be safely loaded or incorporated Within the lamp bulb without the danger of the bulb exploding on charge flashing, with a corresponding limitation on the amount of light-output obtainable from the lamp. To this end, the amount of combustible material per unit volume of bulb space (i.e., the concentration of combustible material in the bulb), and the pressure of the filling gas, in flash lamps as made heretofore, has been maintained within limits of less than around 2 mg. per cc. of bulb volume and less than 2 atmospheres pressure in the case of aluminum type combustible materials, and around 6 mg. per cc. of bulb volume and less than 2 atmospheres pressure in the case of zirconium type combustible material.

It is an object of my invention, therefore, to provide a flash lamp of the general character herein referred to having greatly increased light output per unit volume of bulb space while possessing adequate safety from exploo sion on charge flashing.

Another object of my invention is to provide a flash lamp of the general type referred to which is of many times smaller overall size than any flash lamp heretofore available and which is capable of providing a light flash of sufficient intensity for effective picture-taking purposes.

Still another object of my invention is to provide an extremely small sized flash lamp of the general type referred to and containing a materially greater amount of combustible material per unit volume of bulb space, i.e., a greater concentration, than in any previous flash lamp of such type while at the same time possessing the same degree of safety from explosion on charge flashing.

A further object of my invention is to provide a small size flash lamp of the general type referred to having a bulb many times smaller in size than any flash lamp heretofore available yet possessing a light output per unit volume of bulb space several times greater than the highest level thereof heretofore obtainable in any previous flash lamp.

Briefly stated, according to one aspect of my invention, I have found that by employing a very small size bulb having a volume less than about 2 cc. and consisting of a short length of drawn glass tubing closed at one end by an outwardly protruding integral stem press portion and necked down and tipped off at its other end, and

employing therewith, as the light-producing means Within the bulb, a loose filling of filamentary combustible material consisting essentially of zirconium, it is possible to safely load or charge the bulb with amounts of combustible material per unit volume of bulb space and pressures of filling gas which are many times greater than has been possible heretofore, without the danger of lamp explosion on charge flashing, to thereby obtain a hash lamp having a light output per unit volume of bulb space which is manyfold that obtainable heretofore with flash lamps as previously constructed.

Further objects and advantages of the invention will appear from the following detailed description of a species thereof and from the accompanying drawing.

In the drawing,

Fig. 1 is an elevation, partly in section and on an enlarged scale, of a flash lamp comprising my invention, and

Fig. 2 is an elevation of the lamp at right angles to Fig. 1.

Referring to the drawing, the flash lamp according to the invention comprises a sealed glass envelope or bulb 1 approximately of tubular shape and consisting of a short length of drawn glass tubing closed at one end by an integral flattened external stem press 2 protruding axially from the bulb and necked down and closed at its other end by an end wall portion 3 terminating in an exhaust tip 4. Since drawn glass tubing, as made by conventional glass tube drawing processes, inherently possesses substantially uniform wall thickness throughout, the bulb 1 because of its formation as a drawn length of glass tubing, therefore possesses a substantially um form wall thickness, i.e., throughout at least the tubular extent thereof. In addition, because of its formation as a length of drawn glass tubing, the bulb 1 therefore can be readily made of thicker side wall section than the conventional blown glass bulbs which have been conventionally employed for flash lamps in the past. Thus, in the particular case illustrated, the side wall of the bulb 1 has a wall thickness in the range of about 27 mils whereas the customary blown glass bulbs conventionally employed heretofore for flash lamps have possessed wall thicknesses in the range of around 18 to 20 mils or thereabouts. The bulb 1 is of a size many times smaller, e.g., to 6 times smaller, than that employed in any flash lamp commercially available at present, the bulb having an internal volume of less than 2 cc. and preferably of the order of 1.2 cc., and the tubular portion of the bulb (i.e., the bulb proper), having an outside diameter of the order of A inch and a length of the order of /1 inch. The opposite sides 5 of the stem press 2 are formed as flat surfaces preferably disposed approximately parallel to each other and to the axis of the bulb. As shown, the said flat sides 5 of the stern press 2 are provided with transversely extending guide channelways or grooves 6 for sliding engagement with cooperating guide track means of a lampholding magazine or feeding chamber (not shown) of a lamp flashing apparatus.

Sealed into the stem press end of the bulb 1 is a lamp ignition mount 7 comprising a pair of lead-in wires 8 which, in the manufacture of the lamp, are sealed into the stem press 2 so as to extend therethrough and into the bulb 1 in a. direction approximately longitudinally of the bulb and in more or less side-by-side closely spaced relation. Outwardly of the stem press 2 the lead-in wires 8 are provided with suitable terminal contact portions which may be of the type disclosed and claimed in copendiug application Serial No. 803,637, VaudenBoom et al., filed April 2, 1959 and assigned to the assignee of the present invention, and comprising open wire loop contact members 9 respectively bent around the end of the stem press to extend alongside the opposite flat sides 5 thereof but terminating short of the guide channelways 6 therein. Interiorly of the bulb 1, the lead-in wires 8 are rigidly tied together and held in place by a support bead 19 of glass or other suitable insulating material in which the lead-in wires are embedded. The lead-in wires 3 terminate at their inner ends in the lower region of the bulb near the stem press end thereof so as to be removed from the top or end wall 3 thereof, and they are bridged at their said inner ends by an ignition filament 11 preferably consisting of a short straight length of fine tungsten wire having a diameter preferably of the order of 0.7 mil. The inner tips or ends of the lead-in wires 8 are provided with coatings or beads 12 of a suitable fulminating or primer material which beads 12 are in contact with the filament 11 and become ignited when the latter is energized and heated by the passage of an electric current therethrough. The fulminating material of which the primer beads 12 are composed preferably is of the general type disclosed and claimed in US. Patent 2,280,598, Meredith, issued April 21, 1942, and comprising an admixture of fine powders (i.e., of the order of 325 mesh or finer) of zirconium, potassium perchlorate and No. 3 grade magnesium bonded together by a suitable binder such as a 25% solution of nitrocellulose in amyl acetate. For best results, however, and particularly where the ignition filament 11 is of a diameter of the order of 0.7 mil, it is preferred that the relative proportions of the above-named powder ingredients be within the particular ranges disclosed and claimed in US. Patent 2,756,577, Anderson, issued July 31, 1956 and assigned to the assignee of the present invention, such ranges being of the order of from 90% zirconium, l-8% magnesium, and 935 potassium perchlorate.

The bulb 1 contains a filling of oxygen or other oxygenous combustion-supporting gas and a quantity of combustible light-giving material 13 which, on ignition by the filament 11 and primer 12 constituting the ignition means of the lamp, enters into a reaction with the filling gas to produce a momentary flash of actinic light of high intensity suitable for picture-taking purposes. In accordance with the invention, the combustible material 13 consists of a loosely distributed quantity of filamentary strands of a readily combustible metallic material consisting essentially of zirconium or an alloy essentially composed of zirconium. The filamentary combustible material 13 preferably is in the form of fine cut strands of a thin foil of the above-mentioned composition, the said fine cut strands being such as that commercially known as shredded foil and produced by the method and appar'atus described and claimed in US. Patents 2,297,368 and 2,331,230, Rippl et al., such shredded foil strands having a width ranging from approximately 0.5 to 1.5 mils and a thickness likewise ranging from approximately 0.5 to 1.5 mils. The filamentary combustible material 12 is distributed loosely within the bulb and as uniformly gamma as possible throughout the space within the bulb above the ignition filament 11 in order to insure the most favorable combustion conditions for the said material.

The oxygen or other combustion-supporting gas is introduced into the bulb 1 through a glass exhaust tubulation at the top end 3 of the bulb which tubulation, after the evacuation of the bulb therethrough and the introduction of the oxygen or other combustion-supporting gas into the bulb, is then tipped off as indicated at 4 to hermetically seal the bulb.

To strengthen the bulb 1 and render it substantially shatterproof on charge flashing, a suitable protective lacquer coating 14 such as cellulose acetate is applied to the outer side of the bulb. The inner side of the bulb may be left bare or unprotected by any such lacquer coating.

As mentioned previously, in the manufacture of flash lamps as made heretofore and employing conventional type blown glass bulbs characterized by relatively thin side Wall areas, the amount of filamentary combustible material per unit volume of bulb space has been maintained at a concentration of less than around 2 mg. per cc. of bulb volume in the case of aluminum type combustible materials and less than around 6 mg. per cc. of bulb volume in the case of zirconium type combustible materials, and the amount of combustion-supporting gas in the bulb likewise maintained below pressures in excess of about 2 atmospheres, in order to thereby limit the intensity of the reaction in the bulb on charge flashing, and therefore the developed pressure in the bulb, to a level sufliciently low to afford the required degree of safety from explosion. This limitation on the concentration of the light-producing reaction materials in the bulb for safety considerations therefore has placed, in turn, a limitation on the light output per unit volume of bulb space produced by prior type flash lamps employing blown glass bulbs In accordance with the invention, however, we have found that by employing a glass bulb 1 having a very small size less than about 2 co. in volume and consisting of a short length of drawn glass tubing whereby, because of the inherent characteristics of drawn glass tubing, at least the side Walls of the bulbs are of substantial, and more or less uniform thickness throughout, i.e., free of thin wall sections, and by the further expedient of employing filamentary combustible material 13 consisting essentially of zirconium which has the characteristic of burning in place within the lamp bulb rather than forming small burning metal particles or globules which are violently flung at high velocities about the interior space of the bulb on charge flashing as in the case of aluminum type combustible materials which have been customarily employed heretofore in flash lamps, it p is possible to safely load or charge the bulb with far greater amounts of light-producing reaction materials (i.e., combustible material 13 and combustion-supporting gas) than has heretofore been possible without the danger of lamp explosion on charge flashing, and to thereby obtain a light output per unit volume of bulb space which is manyfold that obtained by any previous type of flash lamp.

Accordingly, in the flash lamp comprising my invention, the bulb 1 is loaded with filamentary combustible zirconium material 13, having a unit cross-sectional area within the range of approximately 0.5 to 1.5 square mils, to a concentration of at least 15 mg. per cc. of bulb volume and ranging up to as high as 25 mg. per cc. of bulb volume, and is filled with oxygen or other combustion-supporting gas to a pressure of at least several atmospheres. In the case of the preferred form of flash lamp according to the invention, employing a bulb 1 having a volume of approximately 1.2 cc., the bulb is filled with around 24 mg. of zirconiumshredded foil, the individual strands of which have a thickness of about .0008 inch and a width of about .0012 inch, and with oxygen at a pressure of at least approximately 5 atmospheres and 0 preferably ranging between 5-6 atmospheres. Thus, a flash lamp of such specific construction according to the invention has a concentration of filamentary combustible material within the bulb amounting to around 20 mg. per cc. of bulb volume, which is manyfold (i.e., more than thrice) that of any previous type flash lamp. Flash lamps of the above specific construction, having a clear outside lacquer protective coating 14 on the bulb, will generate a momentary flash of light of approximately 7500- 7800 lumen seconds with a peak intensity of between 400,000 and 500,000 lumens and which, through the control of the size of the primer beads 12, will peak at approximately 15 milliseconds following the closure of the electrical circuit through the ignition filament 10 of. a lamp. Thus, the generated light output per unit volume of bulb space of flash lamps according to the invention amounts to well in excess of 3000 lumen seconds per cc. of bulb volume and, in the case of the specific lamp described, amounts to in excess of 6000 lumen seconds per cc. of bulb volume which actually is manyfold, i.e., around thrice, that of any previous type commercially available flash lamp the highest generated light output of which, so far as applicant is aware, has been in the region of 2000 lumen seconds per cc/o f bulb volume. It is also apparent that a flash lamp having the abovedescribed flash characteristics is eminently suited as a light source for use with ordinary inexpensive type cameras not provided with flash lamp synchronizing means and wherein the so-called open-flash method of taking flash lamp pictures is employed, the flash lamp in such case being flashed during the interval when the camera shutter is in an open position such as occurs when a camera shutter set for time or bulb" is actuated.

Although a preferred embodiment of my invention has been disclosed, it will be understood that the invention is not to be limited to the specific construction and arrangement of parts shown, but that they may be widely modified within the spirit and scope of my invention as defined by the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A'flash lamp comprising a sealed bulb consisting of a short lengthof drawn glass tubing of substantially uniform wall thickness throughout and having an external stem press portion extending from and closing one end thereof, the other end of said length of glass tubing being necked down and closed by an end wall portion terminating in an exhaust tip, said bulb having an internal volume of less than about 2 cc., a protective lacquer coating on the exterior surface of said bulb, a filling of a combustion-supporting gas in said bulb at a pressure of at least several atmospheres, a quantity of combustible filamentary strand material loosely distributed within said bulb and consisting essentially of zirconium, said fila mentary strand material having a unit cross-sectional area within the range of approximately 0.5 to 1.5 square mils, the quantity of said filamentary material in the bulb amounting to at least approximately 15 mg. per cc. of bulb volume, and ignition means in said bulb for igniting said combustible material and comprising a pair of lead-in wires sealed through said stem press, said lamp generating a total light output per unit bulb volume of at least 3000 lumen seconds per cc.

2. A flash lamp comprising a sealed bulb consisting of a short length of drawn glass tubing of substantially uniform wall thickness throughout and having an external stem press portion extending from and closing one end thereof, the other end of said length of glass tubing being necked down and closed by an end wall portion terminating in an exhaust tip, said bulb having an internal volume of less than about 2 cc., a protective lacquer coating on the exterior surface of said bulb, a filling of a combustion-supporting gas in said bulb at a pressure of at least approximately 5 atmospheres, a quantity of combustible filamentary strand material loosely distributed 7 within said bulb and consisting essentially of zirconium, said filamentary strand material having a unit cross-sectional area within the range of approximately 0.5 to 1.5 square mils, the quantity of said filamentary material in the bulb amounting to between 15 to 25 mg. per cc.

of bulb volume, and ignition means in said bulb for igniting said combustible material and comprising a pair of lead-in wires sealed through said stem press, said lampgenerating a total light output per unit bulb volume of at least 3000 lumen seconds per cc.

3. A flash lamp comprising a sealed bulb consisting of a short length of drawn glass tubing of substantially uniform wall thickness throughout and having an external stem press portion extending from and closing one end thereof, the other end of said length of glass tubing being necked down and closed by an end wall portion terminating in an exhaust tip, said bulb having an internal volume of approximately 1.2 cc., a protective lacquer coating on the exterior surface of said bulb, a filling of oxygen in said bulb at a pressure of at least approximately atmospheres, a quantity of combustible filamentary strand material loosely distributed within said bulb and consisting essentially of zirconium, said filamentary strand material having a unit cross-sectional area within the range of approximately 0.5 to 1.5 square mils, the quantity of said filamentary material in the bulb amounting to around 20 mg. per cc. of bulb volume, and ignition means in said bulb for igniting said combustible material and comprising a pair of lead-in Wires sealed through said stern press, said lamp generating a total light output per unit bulb volume of at least approximately 6000 lumen seconds per cc.

4. A flash lamp comprising a sealed bulb consisting of a short length of drawn glass tubing of substantially uniform wall thickness throughout and having an external stern press portion extending from and closing one end thereof, the other end of said length of glass tubing being necked down and closed by an end wall portion termimating in an exhaust tip, said bulb having an internal volume of approximately 1.2 cc., a protective lacquer coating on the exterior surface of said bulb, a filling of oxygen in said bulb at a pressure of at least approximately 5 atmospheres, a quantity of combustible filamentary material in said bulb consisting of fine cut strands of zirconium foil loosely distributed within said bulb, said strands having a thickness of about .0008 inch and a width of about .0012 inch, the quantity of combustible material in said bulb amounting to around 20 mg. per cc. of bulb volume, and ignition means in said bulb for igniting said combustible material and comprising a pair of lead-in wire sealed through said stem press, said lamp generating a total light output per unit bulb volume of at least approximately 6000 lumen seconds per cc.

References Cited in the file of this patent UNITED STATES PATENTS 2,272,059 DeMargitta Feb. 3, 1942 2,289,876 DeMargitta July 14, 1942 2,315,099 Van Liempt Mar. 30, 1943 2,756,577 Anderson July 31, 1956 2,791,112 Skaggs May 7, 1957 

